Background and Aim: New-onset atrial fibrillation (NOAF) is a common condition in critically ill patients, yet the evidence on optimal NOAF management and outcomes is limited. This study evaluates the impact of management strategies on short- and long-term outcomes in patients who develop NOAF during their intensive care unit (ICU) stay. Methods: A retrospective, single-centre study was conducted of all patients with NOAF admitted in a multidisciplinary ICU between 2020 and 2023. The clinical characteristics and outcomes of the patients were collected. The endpoints included the characterisation of management strategies, short-term outcomes during ICU stays (including atrial fibrillation [AF] recurrence), and long-term outcomes after discharge (including AF recurrence and a composite of death or cardiovascular hospitalisation). Results: A total of 160 patients developed NOAF (mean age 69.5 ± 11.8 years; 63% male). Most had cardiovascular comorbidities and high illness severity, with frequent mechanical ventilation (87%) and vasopressor (89%) use. Rhythm-control strategies—predominantly amiodarone—were associated with lower in-hospital AF recurrence (OR 0.28, p = 0.044) and a numerical reduction in post-discharge recurrence. Anticoagulation was initiated in 45% of patients and continued at discharge in 44%, without major bleeding. ICU and in-hospital mortality were 33% and 43%, respectively. During a median follow-up of 10 (range 0–56) months, post-ICU discharge AF recurrence occurred in 34% of patients initially discharged in sinus rhythm. Anticoagulation at discharge was not associated with recurrence, while rhythm control in the ICU and absence of in-hospital recurrence strongly predicted reduced post-discharge recurrence (p < 0.001). Nine patients required readmission, mainly for heart failure or ischaemic stroke. The composite long-term outcome occurred in 24 patients (27%). Conclusions: Post-ICU discharge AF recurrence after NOAF was common. Early rhythm-control strategies were associated with lower in-hospital and post-discharge AF recurrence, and individualised anticoagulation appeared safe in this observational cohort. These findings support proactive post-ICU monitoring and risk-adapted management strategies.